Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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Page 1 of 4

1. The operating pressure for refrigerating units using R-12 as a refrigerant is

15 bar

30 bar

8 bar

2 bar

2. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Always more than unity

Any one of the above

Always less than unity

3. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

Water is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

4. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

5. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Near critical temperature of refrigerant

Above critical temperature

Much below critical temperature

6. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

7. Cooling water is required for following equipment in ammonia absorption plant

Absorber

Condenser

Evaporator

Condenser, absorber and separator (rectifier)

8. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Saturated liquid

Wet vapour

Dry saturated vapour

9. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant pressure

Takes place at constant temperature

Takes place at constant entropy

Involves no change in volume

10. The boiling point of ammonia is

-33.3°C

-77.7°C

-30°C

-10.5°C

Page 2 of 4

11. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.67

0.6

0.376

12. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Zero

Negative

Positive

None of these

13. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

2.15

1.25

14. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Superheat the vapour

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

15. The freezing point of sulphur dioxide is

-77.7°C

-135.8°C

-56.6°C

-75.2°C

16. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Ammonia

Carbon dioxide

Freon

17. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Less

Equally

18. A bootstrap air cooling system has

Two heat exchangers

Three heat exchangers

Four heat exchangers

One heat exchanger

19. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

20. Freon group of refrigerants are

Toxic

Non-inflammable and toxic

Nontoxic and non-inflammable

Inflammable

Page 3 of 4

21. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Normal cooling

Super-cooling

None of these

Sub-cooling or under-cooling

22. Rating of a domestic refrigerator is of the order of

10 tons

40 tons

5 tons

0.1 ton

23. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 3

1: 9

1: 1

9: 1

24. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

More for small capacity and less for high capacity

Less

25. The domestic refrigerator uses following type of compressor

Axial

Piston type reciprocating

Miniature sealed unit

Centrifugal

26. The curved lines on a psychrometric chart indicates

Dew point temperature

Dry bulb temperature

Relative humidity

Wet bulb temperature

27. The capillary tube, as an expansion device, is used in

All of these

Water coolers

Room air conditioners

Domestic refrigerators

28. For obtaining high COP, the pressure range of compressor should be

High

Low

Any value

Optimum

29. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Refrigerant cooling tubes

Condenser tubes

Evaporator tubes

30. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

Page 4 of 4

31. Which of the following cycles uses air as the refrigerant?

Stirling

Carnot

Ericson

Bell Coleman

32. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Reversed Rankine

Carnot

Rankine

33. Critical temperature is the temperature above which

Water will never evaporate

A gas will immediately liquefy

A gas will never liquefy

Water will evaporate

34. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Wet bulb temperature of air

Dew point temperature of air

Dry bulb temperature of air

35. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Low boiling point

Good electrical conductor

Large latent heat

36. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

3.33

4.33

2.33

1.33

37. Most thermostatic expansion valves are set for a superheat of

20°C

15°C

5°C

10°C

38. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

(B) Heat stored in the human body

39. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

None of the above

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

40. In a refrigeration system, the expansion device is connected between the

Evaporator and compressor

Compressor and condenser

Condenser and receiver

Receiver and evaporator

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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